This invention relates to a mold for making elastomeric O-ring seals. More specifically, it relates to a mold defining an O-ring cavity in which the mold sections have parting lines positioned at a 45.degree. angle from a plane passing through the inside and outside diameters of the O-ring.
A conventional prior art mold is illustrated in FIG. 1 of the drawings and comprises an upper mold half 12 and a lower mold half at 14, which, in mating relationship, define the O-ring annular cavity 16. In the manufacture of O-rings, an excess amount of elastomeric material is placed upon the lower mold half, with the upper mold half being brought downwardly under substantial force to compress most of the material into the cavity 16. The excess material is merely compressed between the mold halves and upon curing, extends as flash 18 around the inside and outside diameters of the O-ring depicted in FIG. 2. Unfortunately, the inside and outside diameters are usually the critical sealing surfaces of the O-ring and require that the flash be removed. Various methods have been developed for removing the flash and include tumbling in dry ice; machine trimming, and other methods. Such removal may result in tolerance problems and adverse effects upon the sealing surface.
To overcome these problems, the prior art has suggested the manufacture of an O-ring in which the flash is displaced from the inside and outside diameters of the O-ring. In an article entitled "Sealing Points Free of Flash Eliminate Packing Ring Leakage," appearing in the Aug. 2, 1945, issue of American Machinists, Mr. Harry Wessel not only suggested the desirability of such an O-ring, but also set forth a mold for its manufacture. This mold 20 (depicted in FIG. 3) included a lower mold half 22 having a frustoconical recess and an upper mold half 24 having a mating projection, the inclined surfaces defining a mold cavity 26. The O-ring formed in this mold 20 is depicted in FIG. 4 and has flash 28 extending in a 45.degree. angle from a plane passing through the internal and outside diameters of the O-ring.
Use of the mold at FIG. 3 in conjunction with compression molding techniques may still result in undesirable O-rings. Though the flash at the I.D. and O.D. has been eliminated, an excess amount of seal composition may preclude the mold halves of 22 and 24 from fully seating, thus resulting in an O-ring having an out-of-round cross-section as depicted in FIG. 5.